Deconstructing the home theater pre-processor

Ahhh….the home theater pre-pro….my thoughts on them are basically summarized by the phase “can’t live with them, can’t live without them”! Modern pre-pros are the brain of all modern home theaters. An AVR (audio video receiver) is essentially a pre-pro and multi-channel power amplifier in one box. Pre-pro’s do a number of essential things without which it would be virtually impossible to watch movies in surround sound.

They are not without their limitations though. The main thing that seems to suffer in lower priced units from Marantz and Integra is sound quality. What do you really expect if the the pre-pro manufacturers at this end of the market are basically caught up in a features war that each year adds more functionality to them that most people probably don’t want or need. Audio and video quality is pretty much secondary to discussions of Audyssey XT vs XT32 and 7.1 vs 9.1. The other main problem with pre-pros is that the pace of change, particularly in video, media streaming and room correction is rapid, and makes new pre-pros into obsolete and expensive boat anchors very quickly. Top notch pre-pros are expensive – for example the DataSat RS20i probably classifies as state-of-the-art: 16 channels of output capability, Dirac Live room correction, exceptional DACs…but the retail is >$15k!

A state-of-the-art pre-pro with a $$$ price tag: the DataSat RS20i

What if there was a better way to go about including the functionality of a pre-pro in your system? Could it be done in such as way that would make it modular and upgradeable when new improvements in video processing and room correction make their way to market? Many people say a pre-pro is like a mini audio and video computer. If so could we use a home theater PC as a pre-pro?

Before we delve into this subject let’s step back and take a look at what the core functions of a pre-pro are.

The functions of a pre-pro

Core. These are the pieces of functionality that any pre-pro must have in order to do it’s job. We’re assuming that the source signal is digital from a DVD or Blu-Ray.

Source selection

Volume control

Multi-channel digital to analog conversion

Delays and volumes for individual speakers

Upmixing, from 5.1 to 7.1 for example

Bass management

Secondary. There are a couple of items here which are ‘nice to have’ but are not necessary for a pre-pro to function.

Tertiary. Many Japanese pre-pros have a host of other features which are, in our opinion, not really necessary and many people may not even use.

2nd and 3rd zones

Media streaming

Internet radio

The problem with pre-pros

With all of this functionality packed into one box typically something has to give. It seems like it is typically sound quality. It’s interesting to review the pre-pro market. At one end there are the units from the Japanese manufacturers like Marantz and Integra that include everything but the kitchen sink. It seems features are added every year and many of them are not core to audio and video replay. In fact they most likely hinder reproduction quality as every additional piece of functionality added must take budget away from that dedicated to the audio and video circuitry.

The archetypal Japanese ‘kitchen sink’ pre-pro

At the other end there are the units from Classe, Bryston and Anthem that cost ~9k or so. These units are typically streamlined and focus on audio and video playback quality. Many people, however, are wary of purchasing a high end pre-pro as they have a demonstrable history of becoming obsolete very rapidly. Units purchased before the advent of Blu-Ray and HDMI sell for <20% of their retail price. Most of these changes are driven by improvements in video technology, which moves a lot quicker than audio and where changes in HDMI specifications, for example, happen every few years it seems. The core issue I see day to day is that customers make do with a lower performance unit because they do not want to repeat the mistake of having an expensive boat anchor!

Bryston SP3: audio quality first!

Deconstructing the pre-pro part 1: using an outboard video processor

Top manufacturers recognize these fundamental barriers to purchase with higher end pre-pros and have converged on a solution which involves removing video processing. The pre-pro keeps HDMI source switching but does no processing on it. The Bryston SP3, Cary Audio Cinema 12 and Krell Foundation all embody this thinking. Home theaters taking this approach may not include any video processing functionality beyond that included in the display. Those needing processing to optimize their display or upscale / deinterlace HDTV would likely use a Lumagen processor. Their higher end units incorporate multiple legacy and HDMI inputs, likely enough to mean that most customers do not need their pre-pro to include ANY video source switching. People using a dedicated video processor have a relatively low cost upgrade path when any new video display technology is released – for example Lumagen’s 3D upgrade cost <$500. Compare that to having to replace your whole high end pre-pro at a 9k investment! People using a video processor also take advantage of their class leading functionality and ability to improve the picture quality of any display.

Lumagen XS3D – a state of the art video processor!

Deconstructing the pre-pro part 2: using an Oppo with HDMI inputs

Just what are Oppo doing with their new blu-ray players, the BDP-103 and BDP-105? Their thinking is very solid I think: most people only have one or two sources beyond blu-ray (a game console and a cable box for example)…why don’t we add a couple of HDMI inputs and start to make the blu-ray player a pre-pro. Oppo’s year-on-year inclusion of functionality traditionally reserved for pre-pros (volume control, bass management, media streaming) make this a trend that seems likely to continue. Next year I forsee them introducing 5.1 to 7.1 upmixing. Maybe then we’ll see room correction. It’s interesting that they are already working with the Dirac Live algorithm in their new phone.

Oppo’s BDP103 – the first Blu-Ray player with HDMI inputs

Deconstructing the pre-pro part 3: a HTPC redux

HTPCs have to date generally been used to allow storage and rapid access to content in a way which is easier to use than a disc player and a physical DVD or Blu-Ray. You can rip all of your movies and TV shows to the HTPC and also use it to record cable TV, replacing a DVR. Nearly everyone, maybe 99.9% of users, are using their HTPCs with a pre-pro. They hook up their pre-pro or AVR to the PC via HDMI. The HTPC is basically a clever media storage device.

But what if it could do more? What if it could replace a pre-pro entirely? This is the question that we at Acoustic Frontiers are going to investigate. Until recently there was no software available that could replicate the core functions of a pre-pro. This has changed with the availability of JRiver‘s recent releases. JRiver now has bass management, upmixing and 64 bit digital volume control capabilities. It has inbuilt parametric EQ and can support room correction / crossover convolution files from third parties such as AudioLense and Acourate. Although Dirac Live Room Correction Suite does not come in a plug in version you can run that on your PC too. There is even a plugin – MadVR – that seek to replicate what an outboard video processor like the Lumagen does. The stage is now set for a HTPC to replace the pre-pro in your system!

JRiver’s Theater View

There is of course one major component missing that your hardware must provide – a multi-channel digital-to-analog converter. There are a couple of ways to go about this – an internal soundcard within your computer or an external multi-channel DAC. There are many units available from the pro side of the business that could work including the Metric Halo LIO8, Lynx Aurora as well as the ExaSound e28. Or you could use a digital interface and hook up a number of 2 channel DACs, perhaps using different quality units for your left / right and remaining speakers.

With all this power and flexibility the core questions are:

Can a HTPC replace a pre-pro?

Can a HTPC work reliably in this capacity or will it crash, freeze during playback, etc?

Can it sound better than a high end pre-pro when using an external high quality DAC?

Can it replace an outboard video processor?

The experiment begins…an Acoustic Frontiers HTPC proof of concept!

In our demo room we have a 7 channel surround system using Procella Audio speakers. The screen speakers (left, center and right) are the P610s which need an external crossover. There are four subs in a front and rear array, each of which requires a separate signal. The front is comprised of two Procella P10s and the rear of two JL F112s. We therefore need 12 output channels! Our first attempt at getting the demo room up and running was to use a Marantz AV7701 and a Xilica XP-4080. Whilst this resulted in good sound quality it was far short of the DEQX HDP-4 when it was used to drive the left and right speakers in a stereo setup. It was clear the audio quality of the Marantz and Xilica combo wasn’t up to par with the DEQX, and nor should you expect it to be since the HDP-4 is almost double the retail price of the Marantz / Xilica combination.

We therefore wondered what other solutions there might be. A candidate was DataSat, with their RS20i. However that retails for >$15K! We wondered if we could do the same for less, and with greater flexibility. Once we started looking around we came across the HTPC as a potential solution. It would even be possible to try out the same room correction algorithm as DataSat uses – Dirac Live, since they have just released a room correction package that runs on the PC.

So begins the HTPC experiment. Our PC build is based on the CAPS Zuma but uses a larger chassis with an optical drive to allow DVD and Blu-Ray playback from optical media. We are using a Lynx AES16e card and to start with our external DACs will be a DEQX HDP-4 and a Metric Halo LIO8. Can the Acoustic Frontiers HTPC do 12 channels with room correction at 24/96 without crashing? Will it sound better than a high end pre-pro? All these questions and more will be answered in future blog articles.

24 thoughts on “Deconstructing the home theater pre-processor”

1) High end SSPs = $$$$$ and rapid obsolescence .. not the best value .2) Bare bones SSP = $$$$ alone..and with or without say Lumagen VP, you may still come out ahead in terms of cost but overall cost is still relatively high.. and extra component to manage.3) Japan SSP = $$ . http://www.hometheater.com/content/integra-dtc-98-av-processor-page-2 and AVS forum users who are also 2 ch listeners (read: picky about sound) seem to agree that these units offer outstanding value for surround sound duties (my primary need). These same AVS users agreed Integra/Onkyo were not so good for 2 ch listening ( i think weak analog input ) such they had separate pre-amp for 2ch duties (not my need) .. Now 4K is becoming the buzz. but I can live with future upgrade to a similar class model since these SSPs are relatively inexpensive and easily integrated with my URC solution.4) HTPC.. I am interested to see / experience your results. However, can you control with remote and integrate it with a solution like URC?

I know I sound like I am defending my purchase but (without seeing option 4 yet), I am simply stating option 3 represents the best value for me. Of course different strokes for different folks.

1) High end SSPs = $$$$$ and rapid obsolescence .. not the best value .2) Bare bones SSP = $$$$ alone..and with or without say Lumagen VP, you may still come out ahead in terms of cost but overall cost is still relatively high.. and extra component to manage.3) Japan SSP = $$ . http://www.hometheater.com/content/integra-dtc-98-av-processor-page-2 and AVS forum users who are also 2 ch listeners (read: picky about sound) seem to agree that these units offer outstanding value for surround sound duties (my primary need). These same AVS users agreed Integra/Onkyo were not so good for 2 ch listening ( i think weak analog input ) such they had separate pre-amp for 2ch duties (not my need) .. Now 4K is becoming the buzz. but I can live with future upgrade to a similar class model since these SSPs are relatively inexpensive and easily integrated with my URC solution.4) HTPC.. I am interested to see / experience your results. However, can you control with remote and integrate it with a solution like URC?

I know I sound like I am defending my purchase but (without seeing option 4 yet), I am simply stating option 3 represents the best value for me. Of course different strokes for different folks.

1) High end SSPs = $$$$$ and rapid obsolescence .. not the best value .2) Bare bones SSP = $$$$ alone..and with or without say Lumagen VP, you may still come out ahead in terms of cost but overall cost is still relatively high.. and extra component to manage.3) Japan SSP = $$ . http://www.hometheater.com/content/integra-dtc-98-av-processor-page-2 and AVS forum users who are also 2 ch listeners (read: picky about sound) seem to agree that these units offer outstanding value for surround sound duties (my primary need). These same AVS users agreed Integra/Onkyo were not so good for 2 ch listening ( i think weak analog input ) such they had separate pre-amp for 2ch duties (not my need) .. Now 4K is becoming the buzz. but I can live with future upgrade to a similar class model since these SSPs are relatively inexpensive and easily integrated with my URC solution.4) HTPC.. I am interested to see / experience your results. However, can you control with remote and integrate it with a solution like URC?

I know I sound like I am defending my purchase but (without seeing option 4 yet), I am simply stating option 3 represents the best value for me. Of course different strokes for different folks.

Hey Warren, hope you are well and still enjoying the theater we did for you!

I think option 3 is good for most people since with movies there is so much else going on that the sound is only one component of the overall experience, and is in a supporting role for the video. So a pre-pro like an Integra, Marantz is a good bet when combined with a separate higher quality unit specifically for two channel. There are some people out there who critically listen to multichannel music in which case that would probably mean you would go for a nice pre-pro like a Classe or Bryston.

With option 4 it's going to be interesting. The motherboard I am using has an infrared input, and so theoretically you should be able to treat it like any other component for integration with a URC type solution. Whether it turns out that way in practice is another question! Jriver, the software that I will be using for playback on the HTPC has an iDevice app so it can also be controlled via that route.

Ah, an experiment after my own heart. I love it. I have managed to get my combo audio/HT system just about where I want it, though the recent insertion of the DSPeaker Anti-Mode has whetted my appetite for something more sophisticated and effective across the full range. HT is secondary for me to my 2.0, but it is important, so I am looking forward to watching/hearing this experiment. Thanks for posting!

The DSPeaker is a nice device. Are you using the 8033 or the new Dual Core?

Not everyone (including me) philosophically agrees with full frequency range room correction. Room correction is great in the bass range, especially as an alternative to multiple subwoofers or large bass traps. However there are a few key acoustical issues that cannot be dealt with through room correction. See room correction a primer for more.

The HTPC is up and running with 12 channels for our demo room theater so we’ll be able to start experimenting with room correction soon. First priority is to finish installing the acoustic treatment and the final aesthetic touch ups. Once that is done the HTPC project and the write ups will be our next priority!

If you haven’t already you might want to subscribe to our mailing list so you stay up to date with developments as they occur.

I have been doing some research on my own on this very subject when I found your article.

Today there are 100s of products that offer different streaming and other services which are readily available online. You also have the receivers and such that all focus on these gimmicks rather than on what they were designed to do…AUDIO.

In analog you often have several stages to get the audio to where it needs to be. However, in the digital realm you go from a digital component to the ACR or processor which often times performs more tasks than it needs to. Once again, I think the only thing these units should do is to have high quality DACs that convert the sound to analog with as low a noise floor as possible.

Which is why I think that in the digital said we need to no long look at the units as AVS/Processors but more along the lines of a "Digital Stage" and a "DAC Stage". Similar to the experiment that you were doing. However, there needs to be HDMI inputs into the digital stage and optional analog pass through units into the DAC stage.

In my mind a digital stage would essentially be a HTPC with HDMI inputs where one can change out the video card and the software in it. This way you can upgrade the video processor and audio processor over the internet. The end user could choose the room correction system that he/she wanted and so forth. There is simply no reason to have a unit that is as locked up as you commonly see.

As it is now I am looking to build a HTPC with bluray drive or universal drive(if it’s even made) which I will use for all my movies and digital playback. I will also try Dirac in it. I just wish that I could build something like that with HDMI inputs so I could also hook up my DirecTV box and game console.

Nyal,I like your work / experiment on the HTPC. What is the function of the DEQX HDP-4 and the Metric Halo LIO8?Just digital to analog conversion? And how is room correction done? I know that Acourate has a room correction plug-in for Jriver, but how does Dirac works together with Jriver??And a final question: is it possible to use an external source (blu-ray player f.i. a Oppo with Audiopraise Vanity (digital spdif output) modification)?I am looking forward for your opinionsRegardsJoost

The main purpose of the the HDP-4 and LIO8 is to provide digital to analog conversion. I was also using the HDP4 for linear phase frequency and phase correction of the left and right speakers and to provide the required active crossover.

Room correction was done in JRiver using the built in parametric EQ. Measurements were taken using Room EQ Wizard and filters developed from that. I only used EQ below 150Hz.

The HTPC has evolved somewhat since this blog article. I’m not using an ExaSound E28 and Dirac Live multichannel room correction with an additional Xilica XP4080 for crossover of the left, center and right speakers and delay management of the front and rear subs.

I think you could use a external source and route the video straight to the display and the audio into JRiver for processing via the ASIO line in function. You’d need to find a soundcard that would have enough inputs and outputs. I haven’t tried it though, and don’t know anyone who has.

Nyal, for HDPC DAC conversion, could the Oppo 105 be brought into the process with an HDMI Pci-e port? Then, a computer interface such as RME Multiface could bring analog back in from the 105’s analog outs for Dirac processing.

I’m not sure anyone has got HDMI in to a HTPC working. I got an email from one person who had not been successful with his attempt: "I’ve tried to set up an HTPC – client, not server – with no luck on the video side. My Time – Warner cable box would not play video/recordings through the HDMI card on the PC. Copy protection, perhaps? Have you figured a way around this? Until this problem is resolved I don’t believe an HTPC is a viable alternative to a receiver.Configuration for video was: Cable box -> HDMI input on on generic HDMI PCI card installed in PC-> J. River trial -.> video output through HDMI built into MB to Panasonic plasma. I used an Intel MB (now discontinued), low power i7 processor (3770T, expensive and hard to find), RME Multiface, interface and a generic HDMI card."

You’ve mentioned that you are now using Dirac Live + JRiver. When using the two do you disable JRiver’s Room Correction (except for Bass Management) and let Dirac do the correction or do you use a combination of both?

The surround decoding is done by the playback application. In this particular project that means JRiver. JRiver does not have Atmos, DTS.X or other decoding, and will likely never get it, so you will need to send a bitstream to an outboard AVR or pre-pro to do the decoding. That kind of defeats the purpose of the project, and means that you can no longer use a HTPC as a pre-pro with object based audio. For what it is worth we no longer use or generally recommend the approach outlined in this article for a number of reasons, including the decoding issue, lack of external inputs, general lack of reliability, average-to-poor usability, high complexity, etc.

Hi! Guys try using sound card asus xonar stx II with 7.1 analog out. then you will have good alternative to avr! Card has good spec and you can upgrade to burson high end opamps. I recently ditched pioneer lx87, and am slowly building htpc with STX and iriver setup.